In multi-carrier modulation systems, such as OFDM systems, pilot symbols are often embedded at known sub-carrier locations within OFDM symbols in order to facilitate estimation of the channel through which the OFDM symbol has passed. An example of an OFDM system, which employs both scattered pilot signals and continuous pilot signals is that used for the DVB-T standard as disclosed in EN 300 744 Digital Video Broadcasting (DVB) Framing structure, channel coding and modulation for digital terrestrial television ([8]). Continuous pilot signals are pilot signals transmitted at the same relative sub-carrier location within the symbol, whereas scattered pilots are pilot signals transmitted at different sub-carrier locations for each of a set of OFDM symbols, the location of the pilots being repeated for a subsequent set of symbols.
As disclosed in “Mobile reception of 2K and 8K DVB-T Signals,” by Erik Stare, Proceedings of IBC '98 pp 473-478 ([4]) pilot signals can be used in pilot-assisted channel estimation during demodulation of the OFDM symbol. As the pilots only occur at predetermined separated locations in both the frequency and time dimensions, interpolation is used to estimate the amplitude and phase response of the channel at sample points where no pilot carrier has been transmitted within a currently received OFDM symbol. Following both time and frequency interpolation, a sample of the channel frequency response can be generated (fully sampled version) for each sample in the received OFDM symbol. The estimated channel can therefore be cancelled from the received symbol, so that data conveyed by the symbol can be recovered. However, the interpolation can introduce noise into the channel estimate thereby degrading the performance of the receiver.